binding: Adds a comment why SameSizeAsCSSRule needs to derives ScriptWrappableBase.
binding: Adds a comment why SameSizeAsCSSRule needs to derives ScriptWrappableBase.

BUG=235436

Review URL: https://codereview.chromium.org/488063002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@180645 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk